Directly heated thermocouple



JuneY 29, 1948. .1.A. BECKER Erm.. 2,444,027

DIRECTLY -HEATED THERMOGOUPLE l Filed sept. 1, 1944' FIG. l.' /6 I /5 FIG. 3.

332-42 c. Mfr.

M E JA. BECKER Paire: INI/ENTORS.' ZRGR/FFI 7H '5W/ 3/ MSH/VE Wam 6. Mud,

A TTORNE'V Patented June 29, 1.948

UNITED STATES PATENT OFFICEl 2,444,027 DIRECTLY HEATED THERMOCOUPLE I Joseph A. Becker, Summit, John N. Shive, North Plainield, and- Thomas R. Grilith, Madison, N. J., assignors to Bell Telephone Laboratories,

Incorporated, New York,

ANew York N. Y., a corporation of Application September 1, 1944, Serial No. 552,270

(ci. 13e- 4) Claims.

This invention relates to thermocouples and more particularly to thermocouples sometimes known as colinear, directly heated or self-heated lthenmocouples in which the heating current passes directly through the couple.

Thermocouples have been used for the measurement of electrical power at relatively high irequencies. One of the difculties encountered has been the attainment of suflicient sensitivity to allow the measurement of relatively low level power at these frequencies.

An object of this inventionis to increase the sensitivity of colinearlor directly heated thermoments thereof taken in connection with the appended drawings in which:

Fig. 1 shows in section one illustrative embodiment of this invention having a bead of relativelyhigh resistance material at the hot junction;

Fig. 2 shows in section another embodiment of the invention having a. resistance filament at the hot junction; and Fig. 3 shows a measuring circuit employing a thermocouple in accordance with this invention.

In the device illustrated in Fig. 1, the thermocouple comprises'metallic filaments or wires I0 and II of different materials. For example, one wire may be of an alloy comprising nickel and chromium and known as Chromel-P and the other an alloy of gold and palladium. Another combination may comprise an Iiron wire and one of a nickel-copper alloy known as constanten. Various other combinations of metals and alloys that give a thermal electromotive force may also be used.

The ends of the wires I0 and Il may be embedded in spaced relation in a small bead or body I2 of a -high resistivity material to form the hot junction of the thermocouple. A combination of graphite and glass, or of finely divided carbon and aluminum oxide may be employed, the latter combination having been found to be particularly suitable. The outer ends of the thermocouple elements I0 and Il are secured respectively to conductors I3 and I4- and comprise the cold junctions of the thermocouple. `These conductors I3 and I4 are relatively rigid and serve as supports for the thermocouple.

The thermocouple may be enclosed in an` envelope l5 of glassor other suitable material. This envelope may contain air or may be evacuated and sealed oif at the nipple I6. If an air-filled glass envelope is used the conductors I3 and I4 may comprise an alloy of nickel and chromium known as Nichrome. The Nlchrome leads, which do not form a suitable seal with glass, may be cemented to the envelope I5 with sodium silicate, shellac, or other suitable material.

If the envelope is of glass and is to be evacuated, the conductors I3 `and I4 should be of a material that makes an adequate seal with glass. An

alloy of copper,.nickel and iron, known as Cunife is suitable.

It has been found that a thermocouple of Chromel-P and a gold-palladium alloy works well in an atmosphere of air. If a couple of iron and constanten is used, an evacuated envelope is preferred to avoid the liability to corrosion in air of these thenmocouple materials.

The device illustrated in Fig. 2 is similar to that shown in Fig. 1, comprising thermocouple elements 20 and 2l of different metallic materials, support conductors 23 and 24 and an envelope 25 with a. seal-off nipple 26. In this modification the element for concentrating the resistance at the hot junction comprises a filament 22 of carbon.

The thermocouple elements I0 and II of Fig. 1, and 20 and 2l of Fig. 2 may be secured to their respective support conductors by any suitable method or means, a satisfactory one being welding.

The wires from which the thermocouple elements are made and also the carbon filament 22 may be of the order of .0008 inch in diameter. The relatively sti supporting wires I3, I4 and 23, 24 may be of the order of .03 inch in diameter. The units comprising such elements, when completely assembled, are relatively small, the envelope being of the order of 1/ to 'V8 inch long and about .14 inch'in outside diameter.

Colinear or directly heated thermocouples of the .type described may be employed for measuring by connecting the source of high frequency power to -be measured across the conductors I3 and I4 or 23 and 24 and also connecting a direct current measuring means such as a milliammeter across the same conductors, for example, as in Fig. 3, wherein the thermocouple 30 has a source of high frequency power 3l and a direct current meter 32 connected across the leads 33 andv 34. The choke 35 and the condenser 36 restrict the alternating and direct currents to their respective y i circuits.

` I sistance at the vhot junction of .the Ithermocouple,I due `to the presence of: the auxiliary resistance IIBecause of: the concentration of `re- I other. said adjacent endsibelng embedded in close,- I n I ly spaced relationin saidbody of high resistivity I I ematerial, the body completing the hot junction; ,n

I means I|I2 or 22, a large portion of the power to be I I of different materials capable of :forming: a there I xvrncnelectricYjunction,v aportion of each lanient V I being in :close: proximity :to "af corresponding por-I I tion of the ctherillamnt, and means-forconcen-I I I y I Itrating the heating effect of theheating current I I I lin the regionIofI proximityiof said; ilaments. said I2 ments andincontactwltheach. y, I I the passage ,of I

*pourront therethrough comprising: two filaments scope of the appendedclaims only. I I I Whatisclaimedisr' I I `LA thermocouple heated by the,

:atingcurrentat said hot junction. I v'2,'. A .thermocoupie heated Iby Ithe passageof I current therethrough Icomprisinga fliamento I i iron, a .filament of nickel-copper alloy, a. nia,-

ment of carbongImeansI for mounting; said iron, v

and serving to concentrate the heat or the and alloy filaments in substantially colinearre- I lation kwith their adjacent ends slightly Ispaced,I Ii

. vsaid carbon illament being bridgedbetween the I adjacent 'ends of they other nlaments to vform ,the

current therethrough comprisingtwo laments i I hot Junction of the thermocouple, the ,carbon I iilameht servingtoconcentrate the heating eiectv I of the operating current at ,the hot junction. I I

meanscomprising asmall body of relatively high v I 2.' A thermocouple heatedI by I I Iofdiiferent; materials capable of forming, a ther-,-

I vofI the other Iiament :and means Ifor, conseil- Itrating the heating edectcf the-,heatingcurrent in the region of proximityof said iilamentsysaid I I I rmeansvxzomprising alsmall body of relatively high I resistivity material in which said niaments are I I embecdedine1ose1yspacedre1anon- I I a I r 3j. A thermccouple; :heated by tively high resistivity' material in which said filan I resistivity material interposed between the kfila-I n I ments are embedded in closely spaced relation to form said hot junction.

4. A thermocouple heated by -the passage of current therethrough comprising two laments of different metals, means for mounting said iilaments with an end of each in closely spaced relation to the end of the other, and means for concentrating the heating effect of the operating current at a. hot junction comprising a iilament of carbon, bridging the small space between the metal laments, and completing said hot junction.

5. A thermocouple heated by the passage of current therethrough comprising a lament of nickel-chromium alloy, a lament of gold-palladium alloy, a lament of carbon, means for mounting said alloy filaments in substantially colinear relation with their adjacent ends slightly spaced. said carbon filament being bridged between the adjacent ends of the alloy filaments to form the hot junction of the thermocouple, the carbon lament serving to concentrate the heating effect of the operating current at the hot junction.

6. A thermocouple heated by the passage of current therethrough comprising a -filament of nickel-chromium alloy, a lament ofvgold-palladium alloy, a small body of high resistivity material, and means for supporting the laments with one end of each adjacent an end of the 8. ,A thermocoupie heated bythe passagecf 4I I current therethrough comprising, a nlament of I `iron, anlament: ofnickel-fcopper allena. small ,I

body of high kresistivity material,v and means for ISullporting; the :filaments with one, end of each I adjacent Ian end of thecthensaid adjacent ends; I being embedded ,in closely spacedreiation in said'y I f I body of high resistivity material. the body comI y I I pletingthe vhot Junction andgserving tcfconcen; I I n trate the heat ,of theoperating current :atsaid: ,I 'I mojelectricuncticn, aportiongof eachfilamentbe: I I hotijunction. I I I I I y I y I ing in close proxinzhltytoacorresponding portion, I j I ,I I ,9; rA thermoggupfe heated by zthe passage of I y I current therethrough vcomprising I twov filamentsl 1 I I of differentmateriais capable or forming a ther- I I vI:mcelectnc Junction, a, portion,ci'Ieach :filamenti 1, I being in close, proximity to a corresponding por-1 y I I tion of; the otherfllament, and, means, for con-I I I ,I 1 centrating ythe heating feifect, of the heating,cur-

rentinthe region; of proximity I'of said;filaments, I 1 I Isadmeans comprising a small ,body of finely di- I y 1 vided carbon andaiuninumoxide in which said, I fliaments are embedded; inlclosely spaced r'eIatiQLn.I j l 10,;In a thermoccupleheatedby ,thepassage I of current therethrough for measuring high; fre,, y quency pcwerand comprising twonlaments ofv different material capable of forming a thermoelectric Junction, a portion of each iilament being in close proximity to a corresponding portion of the other filament. means for increasing the sensitivity of said thermocouple by concentrating the heating effect of the heating current in the region of proximity of said filaments, said means comprising a small body of relatively high resistivity .material interposed between the filaments and in contact with each.

JOSEPH A. BECKER.

JOHN N. SHIVE.

THOMAS R. GRIFFITH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS OTHER REFERENCES Kipp et al., Instruments, August 1931, p. 472. 

